1. strictures
Strictures are rules or restrictions. In this passage Heather is giving herself some rules she must follow about her diet so that she can do the best in her training and her race.
2. rigorous
A rigorous regimen is one that is specific, strict and difficult. Here Heather needs to have a rigorous training regimen if she's hoping to do well in a marathon, or even finish.
3. pinnacle
The pinnacle is the peak or climax. Since Heather wants to be at peak performance for race day, pinnacle is the best fit for this blank.
4. conducive
Something that is conducive is helpful or at least not hindering something. Here it says that if she rests before her race, it will help her win. That's true.
5. sedentary
A sedentary person is one who is basically a couch potato. They sit around all day doing not much. Since it says that if she's not sleeping, she will be running. She is most definitely not sedentary. This fits because the sentence is saying that no one will call her sedentary.
